1. Field of the Invention
The present invention relates to devices for clamping tubular members together and particularly, to interior clamps for locking the extended sections of telescoping extension poles in place.
2. Description of the Prior Art
Extension poles are used in a number of fields, for example, in connection with washing windows, where the reach of the operator needs to be extended in a safe manner. Window washers employ squeegees and other cleaning utensils to clean windows precisely, sometimes at considerable heights, and occasionally they need to use extension poles of varying lengths to extend their reach without changing the operator's position. For that purpose window washers have used telescopic extension poles, which are a series of concentric tubes of increasing diameter stored within each other so that as additional length is needed, a tube with a smaller inner diameter is pulled out and extended to the desired length.
Various devices have been used to lock the sections of the extension pole at their desired position. One clamping method which has been used to join the sections of the extended pole is a cone clamp. This device can be used to obtain a solid, securely locked telescopic joint. It includes a sleeve with longitudinally projecting ridges and radial threads which is permanently mounted on the exterior of a larger diameter pole; the inner pole is extended out and a cone is tightened over the sleeve. Internal threads on the cone engage with matching threads on the sleeve and as they are screwed together, the clamp tightens on the pole and holds the joint in place. Although it provides a secure locking mechanism, this form of clamp requires projections which are permanently anchored to the tube and a conical attachment along the exterior surface of the tubes at their joint. As the extension pole is pulled through the user's hand during use, these projections at the joint can irritate the hand.
To avoid such irritation, many window washers and other persons prefer to use extension poles with an interior clamping device because it allows the poles to have a smooth surface on the exterior joint during use, as well as when it is in a telescoped or collapsed position. Various types of internal clamps, with all the parts located on the interior of the poles, have been developed. In one type, a projecting cylindrical plug with eccentric stops is mounted in the end of one tube. Slotted rings having indentations to match the stops are fastened onto the plug. When the tube is rotated the rings move slightly off-center and jam against the interior of the other tube. In another variation, the projecting plug has an eccentric indentation with a stop and a slightly oval ring of uneven width to fit over the eccentric section; rotation of the pole causes the oval ring to move off-center and fill the space in the pole. Another version of inner clamp utilizes an oval-shaped plug placed inside a circular plug in the pole; as the pole is rotated, one plug distorts the other and puts pressure against the inner wall of the tube. While all these centric-type clamps do create a smooth exterior surface of the poles, there are various disadvantages to their use. Generally, the eccentric plugs cannot be rotated through more than one rotation of the pole, which thus limits the amount of pressure which can be applied and the control the user has over the locking joint. Since many of these clamps do not provide a tight lock to start with, the eccentric member can usually be dislodged quite easily during the use of the pole as it is subjected to various motions by the window washer and the poles can unintentionally be knocked loose. In addition, the parts of the eccentric clamps inside the telescoping poles have a tendency to break easily and they are then difficult to retrieve for repair.
Accordingly, there has been a need, particularly for window washers and others who operate tools which require an extended reach, to have a telescoping extension pole which can be easily operated to provide a secure controlled lock between the axial extensions of the poles, but yet will also provide a clean, smooth outer surface for engagement with the hands when pulling the pole through the user's hand or when releasing it for a new extension. The present invention provides an interior clamping device which overcomes the problems with the prior art telescoping extension poles. An additional advantage of this invention is that it can be used in other applications where tubular members need to be put together temporarily but securely and where it is desirable to have a smooth exterior surface on the poles, such as the tubular frames used in show displays, or in assembling tripods or in anchoring the squeegee to the extension pole itself. Thus the present invention provides a unique solution to the problems of the prior art of telescopic extension poles and is an invention which can be used advantageously with other applications.